Formation Of Volatile Substances Research Articles

Antioxidant activities and volatile compounds of Chinese cabbage sauce prepared by the combination of Lactobacillus plantarum and functional oligosaccharides

The effects of Lactobacillus plantarum fermentation and addition of fructooligosaccharide (FOS), galactooligosaccharide (GOS) or isomaltooligosaccharide (IMO) on the antioxidant activities and volatile compounds of Chinese cabbage sauces prepared with salt or chilli powder were investigated. Lactobacillus plantarum exhibited excellent growth ability in cabbage sauces and the colony counts remained above 7.70 log CFU/mL throughout the fermentation process. Addition of FOS and GOS significantly promoted Lactobacillus plantarum proliferation remaining above 8.13 log CFU/mL at the end of fermentation. In addition, contents of total phenolic and flavonoid were significantly increased at the end of fermentation, especially for spicy cabbage sauce with oligosaccharides addition. Quercetin content was increased by 88.51% in cabbage sauce after Lactobacillus plantarum fermentation. DPPH radical scavenging activity and FRAP of cabbage sauces were improved by Lactobacillus plantarum fermentation. Contents of gallic acid, caffeic acid, and p-coumaric were positively correlated with antioxidant activities (p < 0.05). Furthermore, a total of 81 volatile compounds were detected in cabbage sauce before and after fermentation, including 22 alcohols, 15 esters, 14 terpenes, 10 ketones, nine hydrocarbons, six aldehydes, three nitriles, and two acids. Total contents of alcohols, esters and ketones were increased by Lactobacillus plantarum fermentation. Terpenes, as new compounds, appeared in fermented cabbage sauce, especially for the fermented spicy cabbage sauces in the range of 1179.98–2428.27 μg/L. Hierarchical cluster analysis indicated that Lactobacillus plantarum fermentation and oligosaccharides addition exhibited positive effects on the formation of volatile substances in Chinese cabbage sauce.

The Role of Amino Acids in the Formation of Aroma-Active Compounds during Shrimp Hot Air Drying by GC-MS and GC-IMS.

In the present paper, the role of amino acids of Penaeus vannamei was investigated in the formation of volatile substances during drying. The variations in volatile substances among samples with different moisture contents (raw, 45%, 30%, 15%, and 5%) were obtained by gas chromatography-ion mobility spectrometry (GC-IMS) and gas chromatography-mass spectrometry (GC-MS). The amino acid contents of the above samples were measured by the amino acid automatic analyzer. Correlation between pyrazines and the various amino acid contents was analyzed by the Pearson correlation coefficient. Their correlation was verified by conducting addition assays. The types and contents of volatile components increased significantly in samples with moisture contents between 30% and 5%. The most obvious increases in the type, content and odor activity value of pyrazines were observed in this range. Basic amino acids (Arg, Lys, and His) had a strong correlation with the formation of pyrazines. Addition assays verified that the addition of Arg and Lys increased the content of pyrazines in shrimp after drying.

Modification of Physicochemical Properties by Heteroaggregation of Oppositely Charged Lactoferrin and Soybean Protein Isolate Coated DHA Emulsion Droplets.

In this study, the effect of heteroaggregation (HA) on the physicochemical stability and the formation of volatile substances of DHA emulsions was investigated. HA-DHA emulsions were produced by combination of lactoferrin (LF)-DHA and soy protein isolate (SPI)-DHA emulsions at pH 6.0. Zeta-potentials, droplet sizes, stability, and microstructures were measured as a function of different ratios of LF-DHA to SPI-DHA droplets. DHA oxidation of single and HA emulsions was determined through measurements of lipid hydroperoxides, thiobarbituric acid reactive substances, and the formation of volatile substances. LF-DHA to SPI-DHA droplets ratios of 5:5, 4:6, and 3:7 formed stable emulsions. The lowest zeta-potential, biggest droplet size, and optimum physical stability of heteroaggregated emulsion occurred at a 5:5 of LF-DHA to SPI-DHA droplet ratio. Microstructure behavior indicated that the HA emulsions (LF-DHA droplets/SPI-DHA droplets = 5:5) formed specific three-dimensional uniform networks. The formation of thiobarbituric acid reactive substances, lipid hydroperoxides, and volatile compounds including hexanal and ( E, E)-2,4-heptadienal decreased in HA compared to single emulsions. The results indicated that the physicochemical stability of DHA emulsions was enhanced and that the formation of volatile substances was inhibited by HA. It thus demonstrated the utilization of HA to improve the stability of bioactive compounds in emulsions.

Thermal decomposition and oxidation of coal processing waste

To expand the database of kinetic parameters used for modeling the ignition of coals and their processing waste, promising coal-water slurry and coal-water slurry containing petrochemicals, studies have been performed on an experimental set-up using thermal gravimetric analysis. The research into coals of various ranks (flame, gas, coking, low-caking, and non-baking) and their processing waste (filter cakes) has yielded the decomposition parameters of the organic matter of coal and the formation of volatile substances as well as the oxidation parameters of the coke residue of all the coals and filter cakes under study. The studies cover the temperature range of the burning processes: 450-1300 K (for low-, medium-, and high-temperature burning modes). We have ascertained the dependence of kinetic parameters (pre-exponential factor and activation energy) describing the thermal decomposition of the organic matter of coal on the rank of coals and filter cakes. The findings show that the kinetic parameters describing the thermal decomposition of the organic matter of coal and its processing waste are practically the same. The thermokinetic parameters of coke residue oxidation are close for all the coals under study but they differ significantly for coke residue of filter cakes. The values of thermokinetic parameters obtained in the research are necessary to devise adequate physical and mathematical models and perform numerical studies (for mathematical modeling) of fuel slurry combustion processes in the combustion chambers of power plants.

Partitioning of Volatile Compounds among Process Liquors, Steam, and Condensates: Thermodynamic Simulations with Applications to the Bayer Process

Because of their potential occupational safety and health implications, the formation of volatile substances is of interest to many hydrometallurgical plants, including alumina refineries using the Bayer process. Rigorous thermodynamic models for various groups of volatile compounds have been incorporated into the database of the Murdoch Bayer liquor model to simulate their distribution among different process streams. Under conditions prevailing in a high-temperature digestion stage of the Bayer process, only hydrogen, low hydrocarbons, and mercury are predicted to be present in the gas phase in significant amounts. The other volatiles primarily remain dissolved in the liquor and are therefore transported to the flash vessels. Flash train simulations confirm that hydrophobic substances accumulate in the vapor phase where they can be destroyed by thermal oxidation. However, large fractions of hydrophilic substances are predicted to dissolve in the aqueous phases. They may therefore be released into the environment when digestion condensate is used for washing and dilution purposes. Mercury constitutes a special case because liquid Hg may precipitate in the first heat exchanger when the condensate/vapor ratio is high.

Characterisation of flavour compounds formed by γ-irradiation of polypropylene

Sterilisation of plastic packaging materials for food, pharmaceutical or cosmetic products with 60Co γ-irradiation in the presence of oxygen can result in the formation of volatile substances. These may subsequently induce off-odours in these materials that might be regarded as negative by the consumers. Trace volatiles and odorous substances of polypropylene, irradiated with 60Co γ rays at 10 and 20 kGy, respectively, were collected and analysed by gas chromatography–olfactometry (GC–O), GC–MS and GC–GC–MS. The methodology was successfully applied for identification of 29 characteristic odorants in a non-irradiated control sample and 38 odorants in γ-irradiated polypropylene samples. Selected odour-active compounds were quantified using GC–GC–MS in combination with stable isotope dilution assays. The quantitative data mirrors the compositional changes in volatile odorous substances from polypropylene during treatment with ionising γ rays in a 60Co-irradiation plant.

Comparison of differently coated SPME fibres applied for monitoring volatile substances in vegetable oils

AbstractCereol Group Center of Expertise, Budapest, Hungary Solid‐phase microextraction (SPME) was developed to determine volatile substances from liquid, gas or even solid materials. This technique has been successfully applied for soil, waste water, blood and urine samples, but in spite of its advantages there are still few applications for vegetable oils. SPME is applicable to determine the aroma and other volatile compounds of the oil, which are characteristic to its origin and oxidative status.In this study the sensitivity and selectivity of some commercially available SPME adsorption materials (polydimethylsiloxane, divinylbenzene, carboxen) were compared. The diverse types of stationary phases were investigated by applying standard oils containing volatile substances from 9‐90 mg/kg concentrations.SPME fibre was placed into the headspace of an oil sample in a 30‐ml headspace vial thermostated at 80 °C for 45 min. The extracted volatile materials were desorbed from the fiber in the injection port of the gas chromatograph at 250 °C. Identification of the extracted compounds is based on pure standards and mass spectra. The reliability of the SPME sampling method was studied by parallel measurements.The 2‐cm long fibre coated with divinylbenzene (50 μm) and carboxen (30 μm) proved to be the most appropriate to determine the volatile oxo‐materials from vegetable oils. The method was successfully applied to follow up the formation of volatile substances (e.g. hexanal, t‐2‐hexenal, t‐2‐heptenal, t‐2‐octenal, nonanal, t, t‐2, 4‐nonadienal, t‐2‐nonenal, t‐2‐decenal, t, c‐ and t, t‐2, 4‐decadienal, 2‐pentylfuran, 1‐octen‐3‐ol) during deep frying in sunflower oil.

Can the water content of dairy products be determined accurately by microwave drying?

Oven drying is the most frequently used moisture determination method. To obtain results faster than heating by convection in classic drying ovens, more rapid heating techniques are used. One of these is drying by microwaves. The result of all drying methods is mass loss under the conditions applied. Only in a few cases does the mass lost correspond exactly to the water content. Mass loss is caused by the evaporation of all volatile matter during the drying process, i.e. not only by the loss of water. Foodstuffs in particular risk decomposition reactions and the formation of volatile substances at higher temperatures. The results of drying processes depend on the drying parameters and are variable, whereas the water content is a specific property of the sample. If the water content is to be determined accurately by a drying process, the drying parameters must be adjusted in a way that the results equal those obtained by a specific method, e.g. the Karl Fischer titration. The dependence on the drying parameters varies for different products. In many cases the levels of a set of parameters can be determined so that the mass lost equals the analysed water content; in other situations a differing but reproducible result can be multiplied by a constant factor to give the reference value. This study shows that, for some dairy products, the water contents found by microwave drying are very close to those determined by Karl Fischer titration.

Těkavé látky při kontinuálním kvašení.

Těkavé látky při kontinuálním kvašení.